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| STScI Analysis Newsletter (STAN)
| Cosmic Origins Spectrograph (COS)
| Space Telescope Imaging Spectrograph (STIS)
| June 2011
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In this Newsletter we provide some updates of interest to
COS and STIS users who will be drafting and submitting Phase 2
HST programs over the next several weeks.
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Using Multiple FP-POS positions with COS observations
The use of multiple FP-POS positions is recommended to improve
the quality of all COS spectroscopic data, especially for
observations using the FUV channel.
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New Options for COS FUV Target Acquisitions
Recent changes to the PEAKXD algorithm allow the use of all
three FUV gratings for dispersed-light target acquisitions with
COS. We discuss these changes and provide instructions for
estimating the exposure time necessary to perform a successful
PEAKXD exposure.
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Operational voltage of Segment B of the COS/FUV detector raised
to mitigate effects of gain sag
On March 10, 2011 the operational voltage of Segment B of the
COS/FUV detector was increased to the value used initially in
SMOV and during routine ground testing. The operational voltage
of Segment A was not modified. This change was needed to
mitigate the effects of gain sag, which had become particularly
severe on Segment B, leading to the appearance of
absorption-like features, i.e. gain sag "holes", in the regions
of the detector illuminated by geocoronal Lyman alpha emission
when observing with G130M settings.
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COS G130M 1055 and 1096 Wavelengths are Corrected for OSM Drift
and Zero-point Offsets
As is the case for other modes, observations done using the new
1055 and 1096 cenwaves of the G130M grating will normally have
their wavelength zero-points corrected using wavelength
calibration spectra, but for these settings there are some
special issues to consider.
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The STIS CCD E1 aperture positions
Observers planning STIS CCD spectroscopy are reminded that use
of the E1 aperture positions may dramatically improve the
quality of their data.
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Need for ACQ/Peak Exposures with Small STIS Slits
As STIS ACQ exposures only center the target in the aperture
with an accuracy of about 0.01", when using a slit 0.1" in
width or smaller, an additional ACQ/PEAK exposure sequence is
strongly recommended. The use of ACQ/PEAK exposures is
described in Section 8.3 of the STIS Instrument Handbook;
however, observers should be aware that APT does
not currently provide any warning if these recommended ACQ/PEAK
exposures are omitted.
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Warning for COS and STIS Target Acquisitions on Systems with
Large Orbital Motions
The cataloged position and proper motion of some visual binaries
with large angular separations and significant orbital motion
may not characterize the target's location to the accuracy required
by the target acquisition aperture. For such objects, a custom
proper motion calculation, tailored to approximate the object's
position and motion at the expected time of the observation is
recommended to ensure the the target will be in the target
acquisition aperture. Timing requirements, such as BETWEENS, should
be specified if needed to ensure that the visit can execute only
when this custom proper motion specification is sufficiently
close to the target's true position to satisfy the recommended
positional accuracy for the type of acquisition specified.
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ETC ID in APT
The ETC ID(s) used to simulate your observations is now a
required field in APT.
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| The Space Telescope Science Institute is operated by the
| Association of Universities for Research in Astronomy,
| Inc., under NASA contract NAS5-26555.
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